Mobile Radio Base Station

ABSTRACT

A mobile-radio base station for a telecommunications system includes vector modulator means for independently controlling the phase and/or amplitude of a plurality of component signals representative of the signal to be transmitted or received, such that when these signals pass through a plurality of antenna elements, a beam is formed in a direction according to the phase relationship of the component signals. The invention also includes interface means allowing other base stations to be coupled to the same antenna, with each base station having independent control of its beam direction. Provision is includes for phase compensation of the signals to correct for errors introduced by unequal and variable component signal path lengths between the base station and the antenna. The vector modulator means is arranged to operate at low power levels, where it can operate more efficiently.

This invention relates to a mobile radio base station for use in atelecommunications system. More particularly, it relates to a mobileradio base station for use in a mobile telecommunications system made upfrom a plurality of base stations that are arranged to communicate to aset of mobile units, wherein the plurality of base stations make up anetwork of cells. The invention finds particular application in suchcellular mobile networks, commonly referred to as mobile telephonenetworks.

Operators of cellular mobile radio networks generally employ individualbase stations, each of which usually includes one or more antennas. In acellular mobile radio network, the antenna directivity is a primaryfactor in setting the coverage area which is generally divided into anumber of overlapping cells, each associated with a respective antennaand base station. Each cell contains a base station which communicateswith mobile radios in that cell. The base stations themselves areinterconnected by other means of communication, usually fixed land linesor microwave links arranged in a grid or meshed structure, allowingmobile radios throughout the cell coverage area to communicate with eachother as well as with the public telephone network outside the cellularmobile radio network.

Normally associated with each base station is an antenna mast upon whichthe antennas are mounted. The siting of such masts is problematic, asplanning permission is needed for each one, and land rental or purchaseadds to the cost of the installation. There is therefore a move to shareantennas and antenna sites amongst operators.

Even then, this can lead to problems. Each operator often has severalantennas associated with each base station, with each antenna providingcoverage of a single cell. There may be typically three or six differentcells being serviced by a single base station. As the number ofoperators increases, each providing its own coverage in these cells,this quickly leads to an unacceptable number of discrete antennasmounted on a single mast. Furthermore, in order to avoid mutualinterference, the antennas require adequate separation and the height ofthe mast may need to be increased, or a stronger structure may need tobe used, to enable the mast to withstand high winds, thus exacerbatingthe problems and leading to greater expense.

A solution to this is for operators to share masts and antennas. Therehas been a tendency for this not to happen, due to technical andlogistical problems. This can result in signals causing interferencebetween operators, and hence have a deleterious effect on systemperformance.

Further, there is a need for operators to be able to adjust the angle ofelevation of the boresight of the antenna, known as “tilt”, for suchpurposes as changing the coverage area of an antenna. This is useful ifthe network structure is changed, for example by the addition of otherbase stations or antennas in the cell. This tilt may be implementedmechanically and/or electrically. “Mechanical tilt” involves physicallymoving the antenna radome, whereas “electrical tilt” is achieved bycreating a phase shift or time delay between electrical signals sent to,or received from, different elements of the antenna.

Different operators generally have different tilt requirements, whichagain makes antenna sharing more problematic. Clearly, if two operatorsrequire different mechanical tilt settings they will not be able toshare an antenna.

Solutions exist that comprise banks of mechanically operated phaseshifters mounted within the antenna radome, that are connected to anarray of antenna elements arranged as a plurality of separate antennas,with each operator having control of one antenna within the radome. Inthis way an operator can control the phase of its signals withoutaffecting the signals of another operator. These suffer the commonproblems associated with mechanical systems—they can be slow to operateand unreliable. As they are operated in the antenna housing itself, theymust also work at high powers (on transmit) or at very low powers (onreceive). The use of such systems at high powers can result in theunwanted generation of intermodulation products that can de-sensitisethe base station receiver.

Further solutions exist that use electrical phase shifters in theantenna housing, these phase shifters being remotely controllable, andso providing an easy to adjust beam pattern. Another problem with thisapproach is that any phase shifts will apply to all signals transmittedby the antenna, and all signals received by the antenna. Thusindependent control of electrical tilt is not possible.

The above approach to generating a variable angle of electrical tilt maybe applied to changing the beam pattern in the horizontal plane, such asmay be required when an operator wishes to redirect a beam slightly toadjust cell coverage. Again, the same problems associated with the phaseshifters will arise.

It is an aim of the current invention to provide an antenna interfaceable to provide independent control of antenna parameters that alleviateat least some of the problems of the prior art.

According to the present invention there is provided a base station forcommunicating signals between an operator and one or more mobile unitsby means of an antenna system having a plurality of radiating elements,characterised in that:

the system is arranged to process the signals as a plurality ofcomponent signals, each component signal being associated with one ormore radiating elements within the antenna system, and

modulating means are arranged to apply complex weights to the componentsignals such that summation of the component signals results in theproduction of an antenna beam direction dependent on the value of thecomplex weights, and

wherein splitting, combining, and component signal amplifying means isprovided between the application of the complex weight to the componentsignal and the component signal passing through its associated radiatingelement or elements, the splitting and combining means being arrangedsuch that it allows other operators to be connected to the same antennasystem.

The invention is particularly suitable for combining independent signalsfrom different operators, as each operator requires no knowledge of anyof the signals but its own, in order to control its beam pattern. Anoperator can control its beam pattern—either its receive beam or itstransmit beam—by means of controlling the complex amplitude (i.e. phaseand/or amplitude) of the component signals

Preferably the complex amplitude of the component signals is controlledby means of a vector controller (VC). This is a device that manipulatesa signal by summing together amounts of in-phase and quadrature versionsof itself, the amount of each decided by means of a baseband or lowfrequency multiplier signal, which can have a negative value. In thisway, full control of the amplitude and phase of the VC output relativeto the VC input is possible. However, a VC that is arranged to control,or modulate, only the phase of a signal may be used in someimplementations of the invention.

Controlling the component signals in this fashion allows the electricaltilt of the beam on either transmit or receive to be tailored to therequirements of the operator, if the component signals are provided toan antenna system having spatial diversity in the vertical axis.

Likewise, the invention allows the radiation pattern to be controlled inthe horizontal axis also, if component signals are arranged to beprovided to an antenna system having spatial diversity in the horizontalaxis.

The problems of the prior art, as discussed above, are avoided by meansof this invention, as the phase and amplitude control and adjustment isdone at conveniently low powers, and is performed inside the basestation rather than in a separate unit or in the antenna radome. Thisdoes however mean that there is likely to be more than one connectionfrom the antenna interface to the antenna radome, which will require aplurality of cables or other waveguides.

An antenna system suitable for use with the current invention willtypically comprise an array of elements, these being accessible by thebase station either individually or in subgroups.

The invention provides for the connection of a plurality of basestations to a single antenna system, such that each base station mayhave control of its signals' radiation pattern in either or both thehorizontal or vertical axes. This is done for signals to be transmittedby means of coupling the component signals associated with a particularantenna radiating element or subgroup of elements from each base stationtogether using power combiner means, to provide a composite componentsignal.

For signals that have been received by each elemental antenna element,or subgroup of elements, the signals are separated by splitting meanssuch that each base station is provided with the received signals fromthe antenna elements. Each base station then filters out the signalsrelevant to it in the usual manner.

The splitting and combining means are preferably placed between thecomponent signal amplification means and the antenna system.

The operation of the VC upon the component signals controls thecharacteristics of the beam. The vector sum of the signals transmittedfrom the antenna elements or sub-groups of elements form the beam ontransmit, and the spacing of the antenna elements and relative phaseshift of signals on the elements are factors that define the beampattern that will be formed, in both elevation and azimuth. Otherfactors defining the beam pattern, such as the frequency of the signalbeing transmitted, will be apparent to the normally skilled person.

As the phase of the signals transmitted and received is controlled atthe base station rather than the antenna as with the prior art, it isimportant for the phase control means to be aware of the effect of itsphase control at the antenna. Embodiments of the invention may have theantenna positioned some distance from the base station, and may connectthe two by means of cables, waveguides or similar structures. These canhave an unpredictable effect on the component signal phases. Forexample, any stretching of one cable relative to another will increasethe path length for that cable, and move the phase of the signal at theoutput of the cable. Such stretching can occur due to many reasons, suchas thermal expansion etc.

An antenna as used with the current invention preferably incorporatescalibration means for measuring the relative phases of signals sent toit by the base station. The calibration means would be in communicationwith the base station, which would then have knowledge of both thedesired phase properties of the component signals, and the actual phaseproperties of the signals at the antenna. This then allows the effect ofthe connection means between the antenna and the base station to betaken into account when setting the phases in the VC. Preferably theantenna also includes as part of the calibration means a signalgeneration means for injecting into the receive-path of the systemsignals that can be measured within the basestation. The measurementstaken can be used to compensate for differences in the paths taken byeach of the receive-side component signals.

The calibration means is preferably in communication with all basestations connected to the antenna, such that it is able to be switchedby a base station to be sensitive to the signals generated or receivedby that base station.

According to another aspect of the invention there is provided a methodof controlling the direction of a transmit beam produced by an antennaconnected to at least two base stations, the method comprising:

in a first base station, splitting a first signal to be transmitted intoa plurality of component signals;

applying a complex weight or weights to at least one of the componentsignals, thereby changing the phase and/or amplitude of the componentsignal relative to at least one other of the component signals;

passing the component signals to amplifying and combining means whereinthe signals are brought to a power level suitable for transmission, andthe component signals are combined with component signals from a secondbase station;

passing the combined component signals to antenna elements or groups ofelements, such that transmission by the elements causes a beam of energyrepresentative of the first signal to be formed in a direction governedby the complex weight or weights.

According to a further aspect of the invention there is provided amethod of controlling the direction of a receive beam produced by anantenna connected to at least two base stations, the method comprising:

receiving in the antenna a plurality of component signals, each relatingto a receiving element or group of receiving elements;

separating using splitting and filter means the component signalsintended for a first base station, and amplifying said component signalsusing amplification means;

applying a complex weight or weights to at least one of the componentsignals in the first base station, thereby changing the phase and/oramplitude of the component signal relative to at least one other of thecomponent signals;

combining the component signals in a beamformer in the first basestation to produce a receive beam formed in a direction governed by thecomplex weight or weights.

The invention will now be described in more detail, by way of exampleonly, with reference to the accompanying drawings, in which:

FIG. 1 illustrates in block diagrammatic form a method of the prior artfor controlling the angle of electrical tilt;

FIG. 2 illustrates in block diagrammatic form one embodiment of thecurrent invention for controlling the beam direction using vectorcontrollers within a base station;

FIG. 3 illustrates the concept of applying phase shifts to signalsfeeding an array in order to control the beam characteristics;

FIG. 4 illustrates in block diagrammatic form the invention being usedto couple two operators to a single antenna;

FIG. 5 illustrates in block diagrammatic form detail of a base stationmodulator that incorporates a vector controller, as used in the basebandtransmit-side circuitry of the current invention;

FIG. 6 illustrates in block diagrammatic form detail of a base stationdemodulator that incorporates a vector controller as used in thebaseband receive-side circuitry of the current invention;

FIG. 7 illustrates in block diagrammatic form detail of a vectorcontroller as employed in another embodiment of the current invention,where processing is performed at RF frequencies;

FIG. 8 illustrates in block diagrammatic form details of an embodimentof the current invention, where processing is performed at RFfrequencies for generation of a transmit beam;

FIG. 9 illustrates in block diagrammatic form details of an embodimentof the current invention, where processing is performed at RFfrequencies for generation of a receive beam.

FIG. 1 shows a method of the prior art for controlling the radiationbeam direction for a mobile radio base station system. The methodimplements a variable delay system in the antenna radome. Here, fourchannels are shown, each having an antenna element 1 connected to ameans 2 for controlling the electrical length of the feed to eachelement 1. The electrical length controller 2 implements a variable timedelay in the individual signal paths, such that signals traversing eachpath are all shifted in time by variable amounts. The path lengths areset by a tilt control section (not shown), that provides a tilt controlsignal 4. The signals are split (in the Transmit case) or combined (inthe Receive case) for a single operator A in the distribution network 3.A single, collective input/output 5 is supplied to the distributionnetwork 3 from the base station (not shown). If the antenna elements 1are stacked vertically, then appropriate changing the relative delays ofthe signals on the antenna elements 1 using the delay structure 2 willresult in tilting of the beam pattern. This tilt will occur on allsignals, so if the antenna were to be shared between two or more users,individual control of tilt would not be possible.

FIG. 2 shows a block diagram of one embodiment of the current invention.A mobile radio base station system 6 according to the current inventionis shown connected to an antenna system 7. The connection comprises fourcables 8 a, 8 b, 8 c, 8 d. Each of the four cables 8 carry signals inboth transmit mode and receive mode. The transmit signals are generatedby a transmitter 9. The output of the transmitter is split up into fourequal component signals, and each is fed into a respective vectorcontroller, or phase modulator, 10. The modulators 10 are able to adjustthe relative phase of their input signals such that each output of themodulator may be at a different phase. The component signals from thephase modulators 10 are then amplified in a power amplifier stage 11 andsent through duplexers 12, and through the cables 8 to the antennasystem 7. The base station system 6 includes a splitter/combiner network(not shown) used to allow other operators to connect their base stationsto the same antenna system.

The base station system 6 has receive equipment comprising a set of lownoise amplifiers (LNAs) 13 that each receive component signals from theantenna 7 via the cable structure 8 and duplexers 12. The LNAs then passthe signal to vector controller, or modulator, circuits 14, the outputsof which go to a summer 15, to produce a single, beamformed outputfollowing well-known phased array principles. This passes into thereceiver 19 where it is processed in the conventional manner. Note thatin this embodiment the receiver 19 and the transmitter 9 are state ofthe art items, and would need no significant changes from thosecurrently employed in base station applications. Note also that thenumber of component signals along with their associated amplifiers andmodulators for both transmit and receive shown in this embodiment hasbeen limited to four for clarity—in practice there may be more or lessthan this.

The antenna 7 is similar to antennas used in prior art systems in termsof the radiating element layout. However, whereas existing antennas willcombine the signals from the individual radiating elements into a singleexit port (or sometimes a single port for a particular polarisation), anantenna used with the current invention will provide access to eitherindividual radiating elements or to small groups of radiating elementssuch that by applying signals of differing phase to the individualelements or subgroups of elements, the beam pattern will be controlled.

In transmission, the embodiment of FIG. 2 operates as follows. Datarequired for transmission is configured as an input signal entering thetransmitter 9, which up-converts the signal to a transmission frequency.The output of the transmitter is a low power signal. The up-convertedsignal is then split into (in this example) four component signals bythe splitter 16. Each signal output from the splitter 16 is fed into thevector modulator circuits 10. The modulators 10 are able to adjust thephase and amplitude of the component signal relative to the othercomponent signals. Modulators 10 a and 10 b are arranged to co-operatesuch that they control the angle of electrical tilt of the signaltransmitted from stack #1 of the antenna, and modulators 10 c and 10 dare arranged to co-operate such that they control the angle ofelectrical tilt of the signal transmitted from stack #2 of the antenna.In practice, these angles would generally be the same. Similarly, theangle of boresight of the transmitted signal may be controlled bysetting ah appropriate phase angle between 10 a and 10 d, and between 10b and 10 c. At this point the component signals are at relatively lowpower levels, and therefore it is possible to fabricate a highperformance vector modulator circuit 10 relatively cheaply and easily.The vector modulators 10 are under the control of the beam directioncontroller 17. The outputs of the vector modulators 10 are fed to poweramplifier circuits 11 which amplify the component signals to the correctlevels for transmission. The amplified component signals are then fedvia duplexers 12 and the cable structure 8 to individual antennaelements in the antenna 7, which radiate the signal energy into freespace. The relative phases of the component signals control the beampattern of the resulting composite beam. The duplexers prevent thetransmitted signal from interfering with the receive side of the basestation.

The receive side of FIG. 2 works in a similar fashion. The componentsignals received by the antenna elements within the antenna 7 passindividually from the antenna 7 to the mobile base station system 6, viathe cabling structure 8, where they are fed into duplexers 12, whichfilter out signals at the transmit frequencies and leave just those atthe receive frequencies. The component signals are then individuallyamplified in low noise amplifiers 13. Thus components that follow theLNA 9 need not be critical in terms of their noise performance, as thenoise figure of the system will be largely governed by the LNA 13, theantenna 7 and related cabling 8. The output from each LNA 13 is passedto the vector modulators 14, which, as described above, control thephase and amplitude of the component signals relative to each other,itself under the control of the beam direction controller 17. The phaseand amplitude adjusted signals are then vectorially added together usinga combiner 15, which has the effect of defining a receive beam. Thecombined receive signal is then passed to the receiver 19 where it isthen dealt with in a conventional manner.

The antenna 7 of FIG. 2 has installed a vector measuring receiver (VMR)18, which is able to selectively switch its input to any of the transmitsignals being transmitted, and measure characteristics of that signal.This is desirable in this embodiment, as the antenna 7 is often mountedsome distance from the base station 6, and the cabling structure 8 canbe long enough to distort the phases of the signals passed between theantenna 7 and the base station 6. For example, small temperaturedifferences between the cables will cause their relative lengths tochange due to thermal expansion, and hence will create a phase errorbetween component signals. The purpose of the VMR 17 is therefore tomeasure the individual phases at the antenna, and relay the results ofthe measurement to the base station. The results are received at thebeam direction controller (BDC) 17 where the actual phases at theantenna are compared to the phases as set by the BDC 17. Any error inthe phases caused by the transmission up through the cables 8 can thenbe cancelled out.

This can be further enhanced such that the receive path can becalibrated. To do this, a signal is injected into each of the receivepaths in the antenna housing, such that it produces a set of componentsignals having a known phase relationship. The properties of thesesignals may be measured using the receiver 19 or using a separate,dedicated receiver, within the basestation, and the result used tocompensate for any phase errors using the vector modulators 14. Use of adedicated receiver for this means that the regular operation of theother receivers is not affected.

Note that the embodiment of FIG. 2 shows an embodiment that controls thebeam pattern in a single polarisation governed by the arrangement of theantenna elements. The embodiment is however not restricted to operationin a single polarisation, but could instead be adapted to haveindependent control of beam patterns of orthogonal polarisations. Thiswould involve having separate feeds to orthogonal antennas, with thesefeeds being driven by suitably weighted component signals as per theembodiment of FIG. 2. The versatility of the system may therefore beincreased by increasing the number of component signals, and using theseto control different aspects of the beam

The phases of the component signals required to get a particular beampattern on both transmit and receive are calculated by the beamdirection controller. This has knowledge of the transmission frequency,and also the physical characteristics of the antenna. FIG. 3 a shows avertical stack of elemental antennas e₁, e₂, e₃ that are individuallydriven. If the component signals supplying each elemental antenna e allhave a zero relative phase difference then the resultant beam will betransmitted from the array with no skew—i.e. it will be transmitted inthe direction normal to the plane of the antenna array. If a relativephase shift of θ rad is applied between component signals supplyingsuccessive pairs of antenna elements e with total phase shift increasingcumulatively across the array, then the beam will be directed off fromthe normal by an angle φ rad, given by

$\begin{matrix}{{{Sin}\; \varphi} = \frac{\theta \; \lambda}{2\; \pi \; d}} & {{Eqn}.\mspace{14mu} 1}\end{matrix}$

where λ is the wavelength of the signal being transmitted, and d is theseparation between antenna elements. Such a skewed beam is shown in FIG.3 b.

Equation 1 applies whether the antenna elements are mounted horizontallyor vertically, and so applies to both the boresight and the angle ofelectrical tilt.

FIG. 4 shows an embodiment of the invention arranged to connect morethan one base station to a single antenna, while still allowing eachbase station to have independent control of its beam pattern, both interms of angle of electrical tilt, and beam boresight. Two base stations20, 21 are shown connected to a single antenna 23 by means of an AntennaCombiner Unit (ACU) 22. Each base station 20, 21 is of the type shown inFIG. 2 above, and each operate on different frequencies. The basestation 20 of operator A has a plurality of transmit lines 24, eachcorresponding to a component signal, and each designed to be transmittedfrom a single antenna element or group of elements. The componentsignals on the lines 24 have been suitably modulated in phase andamplitude to achieve a desires angle of electrical tilt. The basestation of operator B has a similar set of lines 25 that are againmodulated to achieve its desired angle of electrical tilt—notnecessarily equal to that required by operator A. Each of the sets oflines 24, 25 from both operators are then combined together in the ACU22. This is done by first band pass filtering each individual componentline 24, 25 in a filter 28, 29 having a characteristic that allows itssignals to pass but blocks the signals of other operator. The componentsignals from each operator that are intended for the same antennaelement or group of elements 26 can then be connected together withoutcausing mutual interference to each other's signals. The combinedcomponent signals are then passed into a duplexer 27, which uses filtersto prevent the transmit signals from interfering with the receivesignals (assuming they are on different frequencies). The combinedcomponent signals are then sent via cabling 30 to the antenna elements26 and transmitted.

A similar process happens in reverse for the receive signals for bothoperators A and B, wherein a plurality of component signals from theantenna elements 26 are passed via the cabling 30 through to theduplexer 27 and individually filtered to separate out one operator'ssignals from those of the other operator. The filtered component signalsare then passed to the appropriate base station where they are combinedusing vector controllers as described in relation to FIG. 2 above.

The combined component signals 30 also go to a vector measuring receiver(VMR) 31 that is able to measure the phase and amplitude of each of thecomponent signals for each operator. At any one time, the VMR 31 isunder the control of the VMR data hub 34, which is itself under thecontrol of one of the base stations 20, 21, which tells the receiver 31which component signal to measure. The data from this measurement isthen sent to the base station where it may be used to apply complexweight corrections to the component signals. Likewise, the receive path,comprising of the cabling 30, duplexer 27, filters 32 and associatedcabling may be calibrated by inserting a signal into each componentsignal path using a switchable signal generator 33, and measuring thesignals in the basestation 20 or 21. Again, these measurements can beused to apply complex weight corrections for the received componentsignals. The signal generator 33 is also under the control of the VMRdata hub 34.

As the modulation of the component signals is done independently by eachoperator on the base station side of the ACU 22, each is able to controlits own beam pattern without having, any adverse effect on the beamsformed by the other operator. Of course, the normally skilled personwill realised that other splitting/combining means may be employed, suchas by using, as appropriate, a network of passive splitters/combinersand filters. Some methods may be more suitable than others, depending onfactors such as the difference in frequency between signals transmittedfrom connected base stations.

FIG. 5 shows in detail one method used to control the component signalssuch that a beam may be controlled. This particular implementation showsa transmit vector controller being used to control the phases of thecomponent signals at a low frequency. The Figure shows detail of twocomponent signal modulators 100, 101. The second channel 101 is ageneralised modulator incorporating a vector controller, and can berepeated for use with subsequent channels.

The modulator 100 comprises a serial to parallel converter connected toa pair of low pass filters 107, each feeding into a digital to analogueconverter (DAC) 200. The analogue output of each DAC 200 goes into amixer circuit 201. The other input to each mixer 201 is from a localoscillator 202. A phase shift of −90° is applied to one of the signalsfrom the local oscillator 202 to one of the mixers 201. The output ofthe mixers 201 are summed to produce a modulated RF output 203. This RFoutput 203 may be at the transmission frequency, in which case thesignal is then passed to an RF amplifier, or it may be at anintermediate frequency (IF), in which case it will undergo a furthermixing stage to take it up to the transmission frequency.

Note that the modulator 100 does not have a facility for phase shiftingits component output. The output of this modulator 100 is therefore thereference output. Modulator 101 is similar to modulator 100 except thatit has a vector controller 106 incorporated to control the phase of theoutput.

The operation of the modulator 100 will now be described. The data to betransmitted enters the modulator as a serial binary stream 102. This isinput to a serial to parallel converter 103 which generates two signalsV1, V2 each representing part of the binary stream 102. V1 and V2 areboth at half of the bit rate of binary stream 102. Each signal isfiltered using a root raised cosine low pass filter 107 to improvespectral efficiency before being converted to an analogue signal V1′,V2′. Note that the presence, and exact type of this filtering isdependent on the particular application the base station is being usedfor.

The filtered signals are then converted to analogue signals, so thatthey can be mixed up to RF frequencies. This is done in an I-Qmodulator, with the first signal V1′ being mixed with a sinusoid, andthe signal V2′ being mixed with a sinusoid separated in phase by 90°from the first. Both resultant signals are then summed to create asingle modulated component signal

Modulator 101 works in a similar way, except it incorporates a vectorcontroller 106. This vector controller 106 works in the digital domain,and takes as its input the same information as used by modulator 100,namely signals V1 and V2. It also takes two control signals, these beinga phase control 108 and an amplitude control 109. The outputs of thevector controller 106 are two signals V3 and V4, these being given by:

V ₃ =K[V ₁ cos φ−V ₂ sin φ]  Eqn. 2

V ₄ =K[V ₁ sin φ+V ₂ cos φ]  Eqn. 3

The phase of V3 and V4 is adjusted by the vector controller such thatwhen the two signals are combined in the I-Q modulator, the combinedsignal has a phase suitably adjusted for forming a desired beam.

Modulator 101 is replicated as necessary for each remaining componentsignal. Although the minimum number of component signals making up theoverall signal to be transmitted is two, finer control of the beampattern can be achieved with more than this, but at added cost andsystem complexity. In practice between two and five are likely to beused. All modulators 100, 101 etc. are fed with a local oscillator (LO)signal 202 derived from the same reference source, and the path from theLO to each I-Q modulator is preferably phase matched. However, if thepaths are not phase matched, the phase error can be corrected byapplying a suitable phase correction weighting in each of the vectorcontrollers 106.

The phase control signal 108 and amplitude control signal 109 that areinput to the vector controller 106 are each derived from two main inputsignals. The phase control signal 108 is calculated from the requiredphase, as decided by the Beam Direction Controller, but this is offsetby a feeder phase correction signal which comes from a Vector MeasuringReceiver (VMR) mounted in the antenna system itself. In this way theerrors introduced by varying lengths of the line to the antenna arecorrected. This mechanism can also be used to correct for any phaseerrors in the LO feed signal to each of the I-Q modulators. Likewise,the amplitude control signal 109 is derived from both a magnitude signalfrom the Beam Direction Controller, and a correction signal from theVMR.

FIG. 6 shows an embodiment of the receive-side beamformer implemented atlow frequencies. Three channels are shown, 110, 111, 112. Each of thesereceive I and Q data from a separate receiver (not shown). Each receiverdeals with the signals from a single antenna element or group ofelements, and so processes a single component signal. The receivers' Iand Q channels are digitised using Analogue to Digital Converters (ADCs)114 114′, after being filtered using anti-alias filters 113, 113′.Channel 110 is a reference channel, and so no phase or amplitudemodulation need be applied to its I and Q signals. Followingdigitisation therefore the I and Q signals are filtered in root-raisedcosine filters 115, 115′ before being input to adders 116, 116′.

Channel 111 is similar to channel 110 except for the addition of avector controller 117 that is able to modulate the phase and/oramplitude of the I and Q channels input to it. The phase and amplitudeis governed by inputs 204 which comprise the required phase value asderived from the theory discussed above, along with any requiredcorrection due to unequal path lengths etc. The outputs of the vectorcontroller 117, i.e. the appropriately phase shifted I and Q channels ofone of the component signals, are then filtered using root-raised cosinefilters 118, 118′ before being fed as another input to the adders 116,116′.

Further channels 112 are provided for processing remaining componentsignals. In practice, it is likely that the number of channels onreceive will equal the number of modulators on transmit.

The outputs of the adders 116, 116′ are the receive beams for the I andQ parts of the received signal respectively. These are then decoded inthe normal manner in decoder 119.

FIG. 7 shows an alternate to the above embodiments, wherein the phaseshifting and beamforming is done at RF frequencies rather than at lowfrequencies. In particular, FIG. 7 shows a component signal vectorcontroller that may be used in the transmit or receive path of a basestation. Looking at the transmit side, an RF signal 120 that has beensuitably modulated with the information to be transmitted is input to aquadrature hybrid 121. This splits the input 120 up into two usefulcomponents—an “in-phase” signal 122, and a “quadrature” signal 123. Eachof these signals 122, 123 is then applied to a multiplier 124, 125. Theother inputs to each of the multipliers 124, 125 are signals S₁, S₂derived from the required phase and magnitude of the component signal.These signals S₁, S₂ are bipolar signals, and by appropriate choice ofS₁ and S₂, the component signal S(t) 126 at the output of combiner 127can be set to an arbitrary phase and amplitude. The modulator of FIG. 7implements the equation:

S(t)=S ₁ cos(2πft)+S ₂ sin(2πft)  Eqn. 4

where S(t) is the output signal, and the input signal has frequency fHz. S(t) can therefore have arbitrary phase depending on the values ofS₁ and S₂. S₁ and S₂ are calculated by the microcontroller 128, based onthe same inputs as used in the vector controller shown in FIG. 5. TwoDACs are used to convert the digital outputs of the microcontroller 128to analogue form suitable for use by the multipliers 124, 125.

FIG. 8 shows how the vector controller of FIG. 7 is embodied in thetransmit section of a base station of the current invention. Thetransmitter modulator 129, oscillator 130 and power control attenuator131 generate an RF signal in the same manner as an ordinary basestation. The RF signal is then split in splitter 132 to generatecomponent signals. A two way splitter 132 is shown, but in practicethere may be more, in order to provide finer control of the beampattern. Each of the component signals is then modulated using thevector controller 133 as detailed above in relation to FIG. 7, beforebeing amplified using power amplifier 134 to a level suitable fortransmission. Each component signal will then be appropriately phaseshifted relative to each other such that when they are fed to theappropriate antenna elements and transmitted, a beam is formed havingthe desired characteristics.

FIG. 9 shows how the vector controller of FIG. 7 is embodied in thereceive section of a base station of the current invention. Thisparticular embodiment is adapted for use in a CDMA, “third generation”system. Two inputs 135, 136 are shown, each of which comes from anantenna element or group of elements, via any splitting arrangementsused to couple other operators to the antenna, and duplexers used toseparate the transmit signal from the receive signal. Each input 135 136is first amplified in a low noise amplifier 137 before being multipliedby a de-correlation code that acts to reduce the incoming bandwidth.Performing the de-correlation before the beamforming improves the systemnoise figure, and so presents a better signal to the phase modulators.Each de-correlated signal is then passed to a vector controller 138,which adjust the phases of the component signals as described inrelation to FIG. 7. The outputs of the vector controllers 138 are thenvectorially summed in the combiner 139, this summing process forming thereceive beam. The resultant signal is then processed by the IF anddemodulator circuitry 140 in the usual way.

The skilled person will be aware that other embodiments within the scopeof the invention may be envisaged, and thus the invention should not belimited to the embodiments as herein described.

1-17. (canceled)
 18. A base station for communicating signals between anoperator and one or more mobile units by means of an antenna systemhaving a plurality of radiating elements, the base station comprising: aprocessor adapted to process the signals as a plurality of componentsignals, each component signal being associated with one or moreradiating elements within the antenna system, and a modulator adapted toapply complex weights to the component signals such that summation ofthe component signals results in the production of an antenna beamdirection dependent on the value of the complex weights; wherein asplitter, a combiner, and a component signal amplifier are providedbetween the modulator adapted to apply the complex weight to thecomponent signal and the component signal passing through its associatedradiating element or elements, the splitter being in a receive signalpath, and the combiner being in a transmit path wherein the splitter andcombiner incorporate an interface allowing independent signals fromwithin the base station, or signals from other base stations, to beconnected, simultaneously to the same antenna system.
 19. A base stationas claimed in claim 18 arranged to apply the complex weights to thecomponent signals at a component signal frequency lower than thecomponent signal frequency that is passed to the antenna.
 20. A basestation as claimed in claim 18 wherein the base station is arranged toapply the complex weights to the component signals at a component signalfrequency substantially the same as the component signal frequency thatis passed to the antenna.
 21. A base station as claimed in claim 18wherein the modulating means comprises vector controllers.
 22. A basestation as claimed in claim 21 wherein the vector controllers arearranged to control the relative phase of each component signal.
 23. Abase station as claimed in claim 21 wherein the vector controllers arearranged to control the amplitude of the component signal.
 24. A methodof controlling the direction of a transmit beam produced by an antennaconnected to at least two base stations, the method comprising: in afirst base station, splitting a first signal to be transmitted into aplurality of component signals; applying a complex weight or weights toat least one of the component signals, thereby changing the phase and/oramplitude of the component signal relative to at least one other of thecomponent signals; passing the component signals to amplifying andcombining means wherein the signals are brought to a power levelsuitable for transmission, and combining the component signals withcomponent signals from a second base station using combining andfiltering means; passing the combined component signals to antennaelements or groups of elements, such that transmission by the elementscauses a beam of energy representative of the first signal to be formedin a direction governed by the complex weight or weights.
 25. A methodas claimed in claim 24 wherein the component signals generated by thesecond base station are independent from those generated by the firstbase station.
 26. A plurality of base stations connected to a singleantenna system, wherein each base station is a base station as claimedin claim
 18. 27. A method of controlling the direction of a receive beamproduced by an antenna connected to at least two base stations, themethod comprising: i) receiving in the antenna a plurality of componentsignals, each relating to a receiving element or group of receivingelements, and passing the signals to splitting and filter means via aplurality of feeder cables; ii) separating using the splitting andfilter means the component signals intended for a first base station,and amplifying said component signals using amplification means; iii)applying a complex weight or weights to at least one of the componentsignals in the first base station, thereby changing the phase and/oramplitude of the component signal relative to at least one other of thecomponent signals; iv) combining the component signals in a beamformerin the first base station to produce a receive beam formed in adirection governed by the complex weight or weights; v) repeating stepsii to iv in a second base station independently of the first basestation.
 28. A base station for communicating signals between anoperator and one or more mobile units by means of an antenna systemhaving a plurality of radiating elements, the base station comprising: aprocessor adapted to process the signals as a plurality of componentsignals, each component signal being associated with one or moreradiating elements within the antenna system, and a modulator adapted toapply complex weights to the component signals such that summation ofthe component signals results in the production of an antenna beamdirection dependent on the value of the complex weights; wherein asplitter, a combiner, and a component signal amplifier are providedbetween the modulator adapted to apply the complex weight to thecomponent signal and the component signal passing through its associatedradiating element or elements, the splitter being in a receive signalpath, and the combiner being in a transmit path wherein the splitter andcombiner incorporate an interface allowing other base stations to beconnected simultaneously to the same antenna system.